Malformed Phonebook Entry Security Vulnerability in RAS Client

ID: Q230677

The information in this article applies to:

Microsoft Windows NT Workstation versions 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3, 4.0 SP4
Microsoft Windows NT Server versions 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3, 4.0 SP4
Microsoft Windows NT Server, Enterprise Edition versions 4.0, 4.0 SP4

SYMPTOMS

Microsoft Remote Access Service (RAS) client software may allow a user with the proper permissions to mount a denial-of-service attack or elevate his or her privileges on a RAS client computer.

CAUSE

This behavior occurs because the RAS client component that processes phonebook entries has an unchecked buffer. As a result, a specially malformed RAS phonebook entry can cause the RAS client to crash.

In very specific conditions, it can cause arbitrary code to run on the client computer. Because the RAS client operates in the security context of the local computer, the arbitrary code also runs in this context. This cannot occur accidentally.

RESOLUTION

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or the individual software update. For information on obtaining the latest service pack, please go to:

http://www.microsoft.com/Windows/ServicePacks/

Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

For information on obtaining the individual software update, contact Microsoft Product Support Services. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

http://www.microsoft.com/support/supportnet/overview/overview.asp

This hotfix has been posted to the following Internet location as Rasffixi.exe (x86) and Rasffixa.exe (Alpha):

ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/hotfixes-postSP5/RAS-fix/

STATUS

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. This problem was first corrected in Windows NT 4.0 Service Pack 6.

MORE INFORMATION

This vulnerability affects only computers running the RAS client software; it does not affect RAS servers. A user must have permission to add or modify phonebook entries to initiate an attack. Permissions can be set using the phonebook's access control list (ACL).

Computers at risk because of this vulnerability are workstations that are configured to dial other computers as servers, including Microsoft Windows NT 4.0, Terminal Server Edition, but are not typically configured to act as RAS clients. This vulnerability affects only local computers; a user cannot directly attack remote computers.

For additional security-related information about Microsoft products, please visit the following Microsoft Web site:

http://www.microsoft.com/security/

Additional query words:

Keywords : kbbug4.00 kbfix4.00
Version : winnt:4.0,4.0 SP1,4.0 SP2,4.0 SP3,4.0 SP4
Platform : winnt
Issue type : kbbug